Characterization and reuse of SiC flakes generated during electrochemical etching of 4H-SiC wafers

Silicon carbide porous flakes are obtained during electrochemical etching (ECE) of n-doped 4H-SiC wafers. In particular, the use of high current conditions (50-500 mA cm-2) causes detachment of silicon carbide residues from the surface of the etched wafers. Herein, comprehensive material characterization demonstrates the possibility of collecting and using these secondary products of the SiC ECE process. In particular, etching of the two different 4H-SiC faces (Si-face and C-face) results in producing porous flakes, characterized by different structural and chemical properties as investigated using N2 adsorption isotherms, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS). Adsorption properties in a water environment were investigated using different classes of dyes (cationic, anionic, and neutral) such as methylene blue, methyl orange, rhodamine B, rhodamine 6G, and thiazolyl blue tetrazolium. The preferential adsorption of the positively charged species well confirms the negative surface charge of the flakes, even though other factors such as steric hindrance and charge screening influence the dye-flake interaction. Methylene Blue (MB) is the most efficiently adsorbed dye and is used as a model to study the adsorption mechanism on both Si and C-face flakes by a thermodynamics and kinetics investigation. The Langmuir model best describes the adsorption mechanism of MB by Si-face generated flakes whilst both Langmuir and Freundlich models fit well the C-face flake adsorption behavior and the kinetic study indicates that the diffusion stage of adsorption is faster than the dye-dye stacking. This preliminary study of the properties of SiC flakes demonstrates their applicability in environmental applications as adsorbent materials whose activity can be mastered by coupling the SiC photocatalytic properties. Moreover, their intrinsic porosity makes possible the dimensional scaling down of these SiC flakes by mechanical sonication to produce SiC nanoparticles as alternative approaches to high-energy ball milling, carbothermic reduction, or laser ablation.